Preferred Stock and Common Stock Warrants - Warrants (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)
Warrants
Loss recognized on revalued warrants	$ 1,641	$ 1,838
Common Stock Warrants
Warrants
Term of warrants (in years)	3 years	3 years
Number of trading days to exercise prior to expiration term		60 days
Number of consecutive trading days to exercise warrants prior to expiration term		90 days
Minimum conversion price percentage		175.00%
Loss recognized on revalued warrants	$ 1,600	$ 1,800